6801 SEAWAY BLVD Geotech Report 2025-08-19

Seaway Commercial Center Subsurface Exploration, Geologic Hazard, 7007 Seaway Boulevard and Geotechnical Engineering Evaluation Everett, Washington Geologic Hazards and Mitigations The Washington State Department of Ecology (Ecology) Construction Stormwater General Permit (also known as the National Pollutant Discharge Elimination System [NPDES] permit) requires weekly Temporary Erosion and Sedimentation Control (TESC) inspections and turbidity monitoring of site runoff for all sites that are one or more acres in size that discharge stormwater to surface waters of the state. The TESC inspections and turbidity monitoring of runoff must be completed by a Certified Erosion and Sediment Control Lead (CESCL) for the duration of the construction. Requirements for inspections, sampling, and reporting can be found in the Construction Stormwater General Permit online at ecology.wa.gov. In order to meet the current Ecology requirements, a properly developed, constructed, and maintained erosion control plan consistent with local standards and best management erosion control practices will be required for this project. It is often necessary to make adjustments and provide additional measures to the TESC plan in order to improve its effectiveness. Ultimately, the success of the TESC plan depends on a proactive approach to project planning and contractor implementation and maintenance. To mitigate and reduce the erosion hazard and potential for off-site sediment transport, we recommend the following: 1. Construction activity should be scheduled or phased as much as possible to avoid earthwork activity during the wet season. 2. The winter performance of a site is dependent on a well-conceived plan for control of site erosion and stormwater runoff.The site plan should include ground-cover measures and staging areas. The contractor should be prepared to implement and maintain the required measures to reduce the amount of exposed ground. 3. TESC elements and perimeter flow control should be established prior to the start of grading. This should include, but is not limited to, silt fencing, swales with check dams, rocked construction entrance, etc. 4. During the wetter months of the year, or when significant storm events are predicted during the summer months, the work area should be stabilized so that if showers occur, it can receive the rainfall without excessive erosion or sediment transport. The required measures for an area to be "buttoned-up" will depend on the time of year and the duration that the area will be left unworked. During the winter months, areas that are to be left unworked for more than 2 days should be mulched or covered with plastic. During the summer months, stabilization will usually consist of seal-rolling the subgrade. Such measures will aid in the contractor's ability to get back into a work area after a storm event. The stabilization process also includes establishing temporary stormwater conveyance channels through work areas to route runoff to the approved treatment/discharge facilities. December 17,2021 ASSOCIATED EARTH SCIENCES,INC. PEL/Id-20200319E001-002 Page 8